Officers killed, injuries reported after peaceful protest in Dallas: What we know

Shots rang out in quick succession as a peaceful protest in Dallas against police killings took a violent turn Thursday night, leaving 12 officers wounded, five fatally. Two civilians also suffered injuries.

Here's what we know:

President Barack Obama will visit Dallas

Obama will cut short his European trip and visit Dallas early next week, as the city mourns five police officers killed by a sniper.

Dallas mayor says city is safe and can start to heal

In an evening news conference Friday, Dallas Mayor Mike Rawlings said the authorities believe the suspect was a lone attacker and that the city is safe.

Dallas Police Chief David O. Brown said Friday morning that the gunman told negotiators that he acted alone as police attempted to get him to surrender Friday morning. After negotiations broke down, officers attached a bomb to a robot typically used to disarm explosives and detonated it, killing the suspect.

Before Johnson was killed, he told police that he was "upset about Black Lives Matter. He was upset about the recent police shootings. He was upset at white people," Brown said. "The suspect stated he wanted to kill white people, especially white officers."

Johnson did not claim affiliation to any groups, according to Brown.

During the attack, Johnson made an ominous statement to negotiators.

"(He) has told our negotiators that the end is coming and that there are bombs all over the place, in (the) garage and in downtown, so we are being very careful," Brown said.

Brown also said police later found bomb-making materials at Johnson's home.

"We're convinced that this suspect had other plans and thought that what he was doing was righteous and believed that he was going to target law enforcement -- make us pay for what he sees as law enforcement's efforts to punish people of color," Brown said.

After authorities found a journal that suggested Johnson had been practicing detonations, Brown said the shooter "obviously had some delusion."